Remember that your needs are irrelevant in this situation——it isn't your boss's job to make sure you make your car payments or that Big Rocko doesn't break your legs for betting on the Giants to win the Super Bowl（do a little research next time）. Your boss isn't, and shouldn't be concerned with your personal problems; his/her concern is the company. Have written documentation of your accomplishments and responsibilities, as well as your information about your salary surveys. Express clearly what it is you were hired to do, how much you have improved efficiency, and how your increased responsibility has benefited THE COMPANY. Exact figures or percentages of improvement can be impressive to supervisors——it's your job to get them to see the big picture of how much of an asset you are. Let them know what you need to get the job done, and remember to tell them it is negotiable. They like that.
As intimidating as it may seem, if you are prepared and your research and documentation show that you deserve a raise, it is likely that you will be compensated in some way. If your figure is flat out rejected, ask what it would take for you to get a raise, and make a date to discuss the topic again.
Your last resort, of course, is the（gasp）counter-offer. Another company making you an offer is a surefire way to get your boss's attention and show your worth. This is a tricky plan that can backfire if you aren't really prepared to leave, or if you break up into hysterics when you first mention it. Make sure that you do have another job to go to, and that you are truly willing to go, because they just might say "Good luck. Don't let the door hit you where the Good Lord split you." On the other side of the coin, if they do offer you a raise, assess whether the money is worth the extra commitment your company will expect in return. You may just want to take the other offer, especially if it means you'll be playing power forward for the Lakers.